The present invention relates to the inhibition of corrosion of metal surfaces in contact with an aqueous system by the use of an oxygen scavenger which reduces the oxygen content of the system.
In aqueous systems, the presence of dissolved gases such as oxygen and carbon dioxide can cause severe corrosion of metal surfaces in contact with the aqueous system. Such corrosion is likely to be observed in boilers, heat exchangers and injection means for use in oil wells. Oxygen causes pitting of the metal surfaces. While such corrosion may affect only a small area of the metal surface, it is usually concentrated and may cause either metal failure or result in the corrosion products blocking the lines of the system.
For example, in boiler systems, corrosion due to the presence of oxygen may occur in feed lines, the boiler, steam lines, and steam condensate return lines as well as other parts of the system. Dissolved carbon dioxide also contributes to corrosion of steam and steam condensate lines.
In order to inhibit corrosion due to oxygen and carbon dioxide, boiler systems have traditionally been treated with oxygen scavengers and neutralizing amines which, respectively, either react with oxygen or neutralize carbon dioxide. Such oxygen scavengers are referred to in a number of patents.
U.S. Pat. No. 4,067,690 refers to the use of hydroxylamines combined with well known catalysts, e.g., alkali metal hydroxides, as oxygen scavengers.
U.S. Pat. No. 4,278,635 refers to the use of hydroquinone and dihydroxy, diamino and aminohydroxybenzenes and their lower alkyl substituted derivatives as boiler water oxygen scavengers.
U.S. Pat. No. 4,350,606 refers to the use of a hydroxylamine compound and a volatile, neutralizing amine such as cyclohexylamines, morpholine, etc. for preventing corrosion in boiler water systems.
U.S. Pat. Nos. 4,279,767 and 4,289,645 refer to the use of a hydrogen-free solution of hydroquinone and certain neutralizing amines such as methoxypropylamine and diethylaminoethanol as an oxygen scavenger for boiler water and other aqueous media.
U.S. Pat. No. 4,419,327 refers to the use of amine-neutralized erythorbic acid as an oxygen remover or scavenger in boiler feedwater.
U.S. Pat. No. 4,627,921 refers to a method for deoxygenation of water at ambient temperature by adding to the water a reducing agent such as hydrazine, morpholine, sodium sulfite or sodium acid sulfite and passing the resultant solution through an absorbent bed which may be made of activated carbon.
U.S. Pat. No. 4,851,130 refers to a method for removing dissolved oxygen from an aqueous oxygencontaining system by contacting said system with erythorbic acid, erythorbate, ascorbic acid, ascorbate and with activated carbon.